The goal of this project is the development of a scalable n x n electrochemical detector array platform with on- chip amplifiers for massively parallel recordings of quantal transmitter release events. The neurobiological process that this assay will analyze is the process of exocytosis and transmitter release, one of the key processes in brain function and beyond. The molecules to be released are stored at high concentration in membrane-bound organelles. Upon stimulation the contents of these vesicles are released in quantal events through a fusion pore that connects the vesicular lumen to the extracellular space. Understanding the mechanisms of vesicle fusion and transmitter release is of broad medical significance. In the treatment of Parkinson's disease the drug levodopa increases dopamine release from the reduced number of dopaminergic neurons. On the other hand, BoTox treatment exerts its effect through the reduction of transmitter release. In addition to these examples, many other drugs and many molecular manipulations modulate transmitter release in various ways. This regulation of transmitter release occurs not only via changing the number or frequency of quantal release events but also via modulation of quantal size and of the kinetics of release from individual vesicles. To understand the mechanism by which a specific manipulation affects transmitter release it is therefore necessary to perform precise measurements of individual quantal release events, analyze their amplitude and time course and derive characteristic parameters. Conventionally, such measurements are performed by positioning a carbon fiber microelectrode close to a cell (such as a chromaffin cell, a dopaminergic or serotonergic neuron or a PC12 cell) under microscopic observation, stimulate the cell and record a series of release events. The technology developed in this project is adapted from the semiconductor industry and involves the development of a CMOS microelectronic chip for on-chip recordings of single quantal release events of oxidizable transmitter molecules such as noradrenaline, dopamine, or serotonin. The technology will allow the simultaneous recording of single vesicle release events from hundreds of cells without the need for microscopic observation and manipulation, and will thereby provide a high-throughput platform to characterize molecular and pharmacological manipulations. The technology will accelerate the research aimed at understanding the molecular mechanisms of transmitter release and its modulation as well as the development and testing of treatments that act through the modulation of transmitter release. In this way this novel assay platform would provide opportunities to measure quantal release events as neurobiological endpoints and will provide a pipeline for target identification and drug discovery.